The present invention relates generally to AC powered light devices, and more particularly to an AC powered organic light emitting diode (OLED) device.
Organic electroluminescent devices, such as organic light emitting diodes (OLEDs), are currently used for display applications and are planned for use in general lighting applications. An OLED device includes one or more light emitting layers disposed between two electrodes, e.g., a cathode and a light transmissive anode, formed on a light transmissive substrate. The light emitting layer emits light upon application of a voltage across the anode and cathode. Upon the application of a voltage from a voltage source, electrons are directly injected into the organic layer from the cathode, and holes are directly injected into the organic layer from the anode. The electrons and the holes travel through the organic layer until they recombine at a luminescent center. This recombination process results in the emission of a photon, i.e., light.
Large area OLED devices typically combine many individual OLED devices on a single substrate or a combination of substrates with multiple individual OLED devices on each substrate. Applications for large area OLED devices include lighting. For most of these applications, alternating current (AC) power is most readily available. However, OLEDs have rectifying current/voltage characteristics and so are typically operated with direct current (DC) power wired with the correct polarity for light emission. In these applications, AC power is converted to DC power to operate the large area OLEDs.
In many signage applications, the sign or display system comprises a light source, and a covering sheet overlying the light source to define the image or lettering desired. The covering sheet is partly opaque and partly transparent. Light from the light source is transmitted through the transparent regions of the covering sheet but not through the opaque regions. Thus, typically, a covering sheet is required to define the image or lettering desired.